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From: Frank Reed (no email)
Date: Mon May 16 2005 - 23:25:23 EDT
George H you wrote:
"It seems that the British almanac had become unduly complacent, and had
just kept on churning out lunar distance predictions that were no better
than those that had been supplied to Cook by Maskelyne, 90 years earlier,
in spite of the advances in astronomy that had taken place in the meantime."
There's a little more to it than that. The tables for the Moon were improved
several times from 1767 up through 1808 or so. By that date the lunar
distance tables were very good with errors typically as small as 6 to 12 seconds of
arc. But after that, they stopped improving and began a slow decline. The
British Nautical Almanac calculators continued to use tables (Burckhardt's, I
think) prepared way back in 1808 decades later. The predictions of the tables
became steadily worse (I haven't investigated yet whether this decrease in
accuracy was happening linearly with time or perhaps quadratically). This must
have contributed to some extent to the declining use of lunars... but perhaps
it was also a result of that decline.
And:
"Chauvenet is emphatic, in 1868, about the
importance of this matter for US Navy vessels."
He's emphatic, but he was a bit of a voice in the wilderness. It would be
interesting to know how many US Navy navigators ever got around to shooting
lunars and reducing them via Chauvenet's method. By this date it seems that
lunars had already become what they are again today --a good challenge and a test
of a skilled navigator.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
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